1. Field of the Invention
The present invention relates to a wire-rope flaw detector that detects strand breakage and breakage of a wire rope (referred to as a wire-rope flaw portion, hereinafter) for suspending a car such as an elevator car.
2. Description of the Related Art
To date, a wire-rope flaw detector has been configured with excitation iron cores, each having at least two magnetic poles, that are arranged in such a way as to face a wire rope and spaced close to each other, respective excitation permanent magnets embedded in the excitation iron cores, and a detection coil disposed at a place between the two magnetic poles; by magnetically saturating the wire rope by means of the two magnetic poles, magnetic flux is generated at a portion of a flaw such as a strand breakage, and by detecting the magnetic flux with the detection coil, the wire-rope flaw portion is detected; there exists a technology in which two detection coils are arranged spaced a predetermined distance apart from each other, and by making subtraction between the outputs of the detection coils, commonly superimposed noise is cancelled so as to raise the signal-to-noise ratio.
In a wire-rope flaw detector disclosed in Japanese Patent Application Laid-Open No. H9-210968, two detection coils are utilized in order to raise the signal-to-noise ratio. The amount of leakage magnetic flux emitted from a flaw portion is far smaller than the amount of the main magnetic flux that saturates the whole rope, and the distribution range thereof is limited to a space in the vicinity of the flaw portion. On the other hand, the voltage, across the detection coil, induced by a constant amount of interlink magnetic flux is in proportion to the number of coil turns. However, even though the coil is disposed in a region where no leakage magnetic flux is distributed, no effective interlink magnetic flux is obtained; therefore, the size of the coil is limited to be the same as or smaller than a certain size (a certain size is a value that depends on the wire-rope diameter and the wire-rope strand diameter). It is an important point in designing the coil that the number of turns is made as large as possible, with the coil size the same as or larger than the certain size; therefore, as a wire material used for the detection coil, an ultrafine electric wire having a diameter of several tens of micrometers is utilized. Additionally, in order to extend a wire-rope flaw portion detectable range, these coils tend to be formed bent in such a way as to enfold a rope.
In order to wind the ultrafine electric wire without causing any winding unevenness and to form it in an approximately U shape without breaking it, there are required dedicated apparatuses or jigs, worker who have learned the skill, and a certain working time; as a result, the coil becomes a component, whose production cost is relative high, among the components that configure the wire-rope flaw detector. Accordingly, arranging two detection coils, as the wire-rope flaw detector disclosed in Japanese Patent Application Laid-Open No. H9-210968, in order to raise the signal-to-noise ratio, becomes one of the factors that raise the production cost of the wire-rope flaw detector; thus, it has been a problem to reduce the cost. Additionally, arranging two detection coils makes the longitudinal dimension of the wire-rope flaw detector extend, and hence it is one of the factors that hinder the downsizing.